1. Field
The presently disclosed and/or claimed inventive process(es), procedure(s), method(s), product(s), result(s) and/or concept(s) (collectively hereinafter referred to as the “presently disclosed and/or claimed inventive concept(s)”) relates generally to lignin nanoparticle dispersions and/or derivatized lignin nanoparticle dispersions. More particularly, but not by way of limitation, the presently disclosed and/or claimed inventive concept(s) relates to a mild, simple process of preparing lignin nanoparticle dispersions. The presently disclosed and/or claimed inventive concept(s) also relates generally to the compositions and methods of making dispersions of lignin nanoparticle-polymer complexes comprising water dispersible and/or water soluble polymers and derivatized and/or non-derivatized lignin nanoparticles.
Additionally, the presently disclosed and/or claimed inventive concept(s) relates generally to a method of using at least one of the lignin nanoparticle dispersions to impart rinse-resistant adsorption of the lignin nanoparticles to a substrate. Further, the presently disclosed and/or claimed inventive concept(s) relates generally to a method of using at least one of the lignin nanoparticle dispersions and/or dispersion of the lignin nanoparticle-polymer complex to impart rinse-resistant hydrophilic properties to surfaces, or function as a nanoparticle surfactant.
2. Background
Lignin is a complex chemical compound integral to the secondary cell walls of plants and some algae. Lignin is most commonly derived from wood, but it is also derived from secondary sources such as corn stover, grass, straws, and other non-woody sources. As such, lignin is an abundant source of renewable material, second only to cellulose. The major sources of lignin are the various chemical wood pulping processes that generate “liquor” byproducts containing lignin, hemicelluloses, and other extracts that are left over after the cellulose fibers have been separated from wood. Several of the more popular chemical pulping processes over the years have been the sulfate process (commonly referred to as the “kraft” process) and the sulfite process. However, since about 1940 the kraft process has been the dominant process. As of 2008, the kraft process accounted for approximately 90% of the pulp produced by chemical processes, globally generating around 1.3 billion tons of “black” liquor per year.
Until recently, lignin contained in liquors from wood pulping, specifically the “black” liquor of the kraft process, was unable to be effectively extracted and the liquors were often burned as an alternative fuel source. With the advent of new capabilities for extracting lignin from liquor byproducts, e.g., the LignoBoost® technology (Innventia AB) and the LignoForce™ technology (FP Innovations, Point-Clair, PQ) to specifically isolate lignin from the “black” liquor byproduct of the kraft process, an industrial need has emerged to develop value-added products from lignin in order to take full advantage of lignin as a raw material.
Previous attempts to use lignin, especially kraft lignin, for value-added products, led to the discovery of a variety of ways that lignin can be derivatized in order to increase the functionality of lignin. For example, Cui et al. (2013), “Lignin polymers: Part 2,” BioResources 8(1), 864-886, hereby incorporated by reference in its entirety, discloses blocking the phenolic units of lignin via ether formation to increase the thermal stability of kraft lignin so that the lignin can be used in thermoplastic materials.
Lignin derivatives are also disclosed in U.S. Pat. No. 3,956,261, hereby incorporated by reference in its entirety, wherein etherification of the lignin phenolic groups was used to add functional groups, such as carboxylate, to the lignin for specific industrial uses. Blocking the phenolic groups by etherification can also reduce the intensity of the black color associated with lignin obtained from the kraft and sulfite pulping processes, as described in U.S. Pat. No. 4,454,066 and hereby incorporated by reference in its entirety. Alternative methods of derivatizing lignin also include methylolation of lignin using formaldehyde as disclosed in, for example U.S. Pat. No. 5,972,047 and U.S. Pat. No. 5,989,299, both of which are hereby incorporated by reference in their entirety, and graft polymerization of the lignin as disclosed in, for example U.S. Pat. No. 7,691,982, hereby incorporated by reference in its entirety. Additional methods of derivatizing lignin are also reviewed in John J. Meister, Plastic Engineering, “Modification of Lignin”, pps. 67-144. Vol. 60. Polymer Modification: Principles, Techniques, and Applications, Ed. John J. Meister (1st. ed. 2000), hereby incorporated by reference in its entirety. Currently, such methods for derivatizing lignin require intensive processing or the use of organic solvents or hazardous chemicals like formaldehyde, ethylene oxide, and other alkylene oxides.
In recent years there has also been a growing interest in the field of nanotechnology including some interest in lignin nanoparticles. Although naturally occurring lignin nanoparticles have been detected in the ocean as dissolved iron carriers, as disclosed in Krachler et al., Global Biogeochemical Cycles 26, GB3024/1-GB3024/9, (2012), hereby incorporated by reference in its entirety, naturally occurring lignin nanoparticles such as these are rare and not economically feasible to harvest for general applications.
Nanoparticles can have physical and chemical properties that are generally attributable to their nanoscale size. Recently, processes for obtaining lignin nanoparticles have emerged including, for example but not limited to, physical methods based on processes that either use ultrasounds and/or grinders and/or anti-solvents (i.e., solvents in which the product is insoluble) and/or processes that adjust the pH of strong alkaline solutions of lignin, as well as chemical methods comprising, for example, lignin hydroxymethylation and/or lignin sulfonation. See, e.g., J. Gilca et al., “Obtaining Lignin Nanoparticles by Sonication.” Ultrason. Sonochem. 23, p. 369-376, (2015).
Lignin nanoparticles have generally been obtained, however, from lignin aqueous solutions with or without an organic solvent by lowering the pH of the solution under shear, as disclosed in, for example, C. Frangville, Chem. Phys. Chem. 13, p. 4235, (2012) and patent publication CN103275331A, both of which are hereby incorporated by reference in their entirety. Additionally, supercritical carbon dioxide has been used as an anti-solvent to obtain lignin nanoparticles from solutions of lignin in acetone or dioxane, as described in, for example, Lu et al., Food Chemistry, 135, p. 63 (2012) and patent publication CN102002165A, both of which are hereby incorporated by reference in their entirety. Cross-linking agents, such as aldehydes, have also been used to modify lignin nanoparticles, as disclosed in patent publication CN103254452. Additionally, lignin nanoparticle dispersions have been obtained directly from water insoluble kraft lignin by chemical derivatization in water, as exemplified in U.S. Pat. No. 4,957,557, hereby incorporated by reference in its entirety. However, such methods of chemical derivatization in water, including those disclosed in U.S. Pat. No. 4,957,557, require the use of hazardous chemicals like formaldehyde in order to prepare the lignin-based nanoparticles in water.
However, as suggested above, methods disclosed in the prior art for preparing lignin nanoparticles, and dispersions of such, often lack the efficiency necessary to make lignin a cost effective source of raw material, as well as pose safety and environmental risks by requiring the use of organic solvents, such as dioxane, and/or requiring pressurized process components. Additionally, methods disclosed in the prior art generally produce nanoparticle dispersions that contain organic solvent impurities that require further processing and added cost. As such, there exists an industrial need for a cost effective method of preparing lignin nanoparticles in water without the use of solvents or hazardous chemicals. Such lignin nanoparticles would be useful in downstream “value-added processes” and would, therefore, have a better economic use than simply burning the lignin as a fuel.
Methods are disclosed herein that provide economical and efficient methods of preparing stable dispersions of lignin (and/or derivatized lignin) nanoparticles in water. These methods do not require the use of hazardous chemicals and may have less environmental impact than methods currently in the prior art. Additionally, methods are disclosed herein that broaden the scope of available applications for dispersions of lignin nanoparticles and derivatized lignin nanoparticles, such as, for example but without limitation, nanoparticle surfactants as defined below. In particular, disclosed herein is a method of treating substrates (herein also referred to as a “surface” or “interface”) with dispersions of lignin nanoparticles or derivatized lignin nanoparticles whereby the lignin nanoparticles and/or derivatized lignin nanoparticles can impart rinse resistant (as defined hereinafter) adsorption of the particles to such surfaces due to a strong surface affinity (defined herein below) for both inorganic and organic surfaces. In one embodiment, the dispersions of lignin nanoparticles and/or derivatized lignin nanoparticles can impart the properties of lignin or derivatized lignin such as, for example but without limitation, hydrophilicity, hydrophobicity, antimicrobial, antioxidant, anti-soiling, UV-protection, on a substrate. A “substrate”, as used herein, is defined to mean any solid surface on which a coating layer of material may be deposited by means of including, for example but without limitation, adsorption.
A lignin nanoparticle-polymer complex and dispersion thereof is also disclosed herein comprising lignin nanoparticles and/or derivatized lignin nanoparticles and at least one water dispersible and/or water soluble polymer. The lignin nanoparticle-polymer complex, as disclosed herein, can also impart rinse resistant properties to surfaces, wherein the degree of resistance may be strongly impacted by the ratio of the lignin nanoparticles and/or derivatized lignin nanoparticles to the water dispersible and/or water soluble polymer. Additionally, the lignin nanoparticle-polymer complex, as disclosed herein, can function as a tunable nanoparticle surfactant.
A “nanoparticle surfactant” is defined herein as either (a) two materials with hydrophilic and hydrophobic character, wherein at least one of which is a nanoparticle, or (b) as a single nanoparticle having two or more domains with hydrophilic and hydrophobic character, and wherein the nanoparticle surfactant can impart properties normally associated with surfactants. The “tunable” property of the nanoparticle surfactant is defined herein as the ability to modify the type and/or the amount of the polymer in the above-referenced lignin nanoparticle-polymer complex without chemically bonding the water dispersible and/or water soluble polymer to the lignin nanoparticle and/or derivatized lignin nanoparticle. In one embodiment, the lignin nanoparticle-polymer complexes, as described above, can impart properties of both (i) the water dispersible and/or waters soluble polymer and (ii) the lignin, including, for example but without limitation, hydrophilicity, hydrophobicity, antimicrobial, and anti-soiling characteristics depending on the water dispersible and/or water soluble polymer that is used.